A low-noise durable transmissive stamper for multi-layer discs using phase transition mastering

ABSTRACT We developed a negative-type photoresist of WOx film and obtained a low noise groove. We also confirmed a feasibility of the transmissive stamper using the WOx film for multi-layer discs. Keywords: phase transition mastering, stamper, multi-layer, blue laser lithography, UV laser lithography, inorganic photoresist, space layer, forward stacking method 1. INTRODUCTION A considerable number of studies have been made on high-density optical disc mastering using deep UV lithography [1], near field lithography [2] or electron beam lithography [3]. Kouchiyama et al. proposed blue laser lithography (O =405nm, NA0.95) using an inorganic positive-type photoresist of transition metal oxide film [4]. Shintani et al. and Miura et al. proposed blue laser lithography ( O =405nm, NA0.85) using negative-type photoresist of GeSbTe film [5] and ZnS-SiO 2 film [6], respectively. Ito et al. proposed UV laser lithography (O =351nm, NA0.9) using the positive-type photoresist of TeOx-based f ilm [7]. These phase transition mastering (PTM ) techniques achieved an areal density of a 25GB Blu-ray disc (BD) ROM without expensive mastering equipment. On the other hand, it has been recognized that multi-layer recording [8] is very helpful in increasing the entire capacity of a disc. However, multi-layer recording suffers from deterioration in the signal to noise ratio, so it requires a low-noise groove. Th e thickness of the space layer between recording layers must also be accurately controlled, since spherical aberration due to thickness errors causes significant problems for multi-layer recording. Moreover, a disposable plastic stamper, used in the process of making the space layer, incurs much cost. In this paper, we propose a durable transmissive stamper fo r multi-layer discs instead of using a disposable plastic stamper, utilizing UV laser lithography ( O =351nm, NA0.9) with a negative-type photoresist of transmissive WOx film. The low-noise characteristics of the replicated groove from the stamper and improvement in thickness accuracy of the space layer are demonstrated.